It is well-known in the art that electromagnetic waves in the radio frequency spectrum may be linearly, elliptically or circularly polarized. Linearly polarized electromagnetic waves are confined to a single plane extending in the direction of wave propagation and may be oriented at any angle. Electromagnetic waves that are either circularly or elliptically polarized comprise a linear wave rotated about the axis of wave propagation in either a clockwise or counter-clockwise manner. The major axis of an elliptically polarized wave may be orientated at any angle in a manner similar to a linearly polarized wave.
In military applications, it is important that information on the incident electromagnetic wave type, that is, orientation and rotation, be determined as quickly as possible. This information provides an important parameter identifying the signature, or fingerprint, of the electromagnetic wave emitter. Once the wave information has been identified, the emitter that generated the incident electromagnetic wave can be recognized from its signature for purposes of intelligence gathering, homing, emitter sorting, interference reduction, or configuration of an active electromagnetic wave jammer.
Historically, polarimeters have been constructed of a dual channel receiver coupled to a dual orthogonally polarized antenna to measure the power of the polarization components of the incident electromagnetic wave. The measured power of these components identifies the polarization characteristics of the electromagnetic waves. A conventional polarimeter comprises an orthogonally polarized antenna coupled to a pair of phase and gain matched receivers. Identification of the type, orientation and rotation of the incident wave is accomplished by comparing the relative amplitude and phase of the output signals from the dual receivers.
This conventional approach to polarimeter construction has proven to be unsatisfactory as it requires interconnecting two complex and costly phase and gain matched receivers. A further drawback of dual channel matched receiver polarimeters is that the second receiver adds weight to the apparatus and requires additional mounting space. In weight and space sensitive applications, for example, in military aircraft, the weight and space necessary to provide a second receiver for the polarimeter may not be available or, if available, is provided at the expense of other important system components.
Accordingly, there is a need for a signal processing technique for polarization detection that eliminates the need for complex and costly dual channel receivers.